All the history of the photography turns around a principle of optics:
When the light penetrates by a small hole (called pinhole) into a closed and dark space, the image inverted by what is outside forms on the opposed wall.
This process was known already in Antiquity.
Aristote, (Greece, IVth century before J.C.) the sky and the solar eclipses announces through its papers of the use of this technique to observe.
We made special rooms for the painters. The light got through the small holes in the painting of the external walls and threw images on screens of transparent paper tightened inside.
The artist penetrated into the room by a trapdoor in the floor and could copy out the images inverted on the paper.
This technique was called will be on drugs obscura, what gave the term of darkroom which we kept to indicate the main part of the camera.
2. Physical discovery: the lens
In the XVIth century, an optical lens is placed inside the hole, to improve the quality of the image.
In the XVIIth, we see appearing of small "portable" darkrooms. Their lenses had risen on a sliding system allowing to make the development. An internal mirror raised the image.
These darkrooms were mainly used no draftsmen: shielded from a black curtain, they used it to throw an image on a paper sheet, and traced then outlines to obtain a rather faithful drawing of the reality.
3. Chemical discovery: a photosensitive surface
In the XVIIIth century, we discover the photosensibility of certain compounds of silver (as the nitrate and the chloride of silver).
Two English scientists, Thomas Wedgwood and Humphry Davy made the first experiments on the creation of a photographic support. They obtained images, but which lasted only a few minutes before fading... They had not found way to fix them.
From its part(On its side), Jacques Alexandre Caesar Charles, French, dealt with similar works and succeeded in fixing vague and little contrasted silhouettes.
It was necessary to find a way to keep the images in time, by stopping the sensibility of supports in the light…
4. 1826: The first photography by Nicéphore Niepce
By 1826-1827, after eleven years of research, the French physicist Niepce succeeded in photographing the landscape which he saw of his window.
He obtained a cliché reflecting well enough the reality, with nevertheless an exposure time which counted in hours (8 hours!).
The support was a plate of tin, made photosensitive, adapted in Camera Obscura.
Niepce called this process a heliography (of Helios, the sun).
In 1832, Niepce joins to Louis Daguerre ( 1787-1851 ), but he dies in 1833. It is Daguerre who returns the popular process, by developing the daguerreotype in 1839: images realized on plates of copper, plated of silver and handled to be photosensitive. The image is then revealed thanks to vapors of mercury.
The daguerreotype was dear and dangerous, because of the used chemicals. The box with mercury allowed to develop daguerreotypes. A tablet served to put the spirit lamp to warm the metallic small dish containing the mercury. The vapor of mercury rose by the open bottom of the box to settle on the plate arranged obliquely inside. The opening in semicircle, practised on the face before, allowed the operator to follow the development of the plate, through a red glass.
It required a relatively long exposure time: it was necessary to use a chair to paint the portrait of the people, what gave them an air a little stuck as show it Honoré Daumier's caricatures for the newspaper Tumult.
Daguerreotypes were fragile objects. They had often risen in frames to protect them. The produced images were unique: they could not be reproduced. Everybody wanted be " daguerréotyper " it was the fashion in the 1840s … One of the first functions of the photography was so the portrait.
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